Photochemistry of Linear Polyenes Related to Vitamin A. 13-Demethylretinal and 14-Methylretinal

Article abstract of DOI:10.1021/j100439a003

The photochemistry of all-trans-13-demethylretinal (2) and all-trans-14-methylretinal (3) is examined in nonpolar and polar solvents.Upon extended irradiation into the first adsorption band, a photoequilibrium mixture is established that contains a number of isomeric photoproducts.High pressure liquid chromatographic methods are employed to isolate and purify each reaction product, and their adsorption spectral and photochemical properties are examined.Primary photoproducts and quantum yields (ψ_PI of trans -> cis or cis -> trans photoisomerization for all-trans-, 7-cis-, 9-cis-, and 11-cis-13- demethylretinal and all-trans-, 9-cis-, 11-cis-, and 13-cis-14-methylretinal are determined in a nonpolar solvent.The variation in ψ_PI and the relative photoproduct ratios of the isomers of 13-demethylretinal and 14-methylretinal differ from those of the corresponding isomers of retinal.The differences in quantum yields, primary products, and their relative ratios are analyzed in terms of the structural changes resulting from incorporation or removal of the alkyl substituent of the C-13-C-14 carbon-carbon double bond.